The present invention generally relates to a method and system for ultrasonic sealing of food product packaging. In particular, the present invention relates to a method and system for directly forming and ultrasonically sealing food product packaging around a food product.
Food products are typically packaged in packaging materials for distribution to consumer markets. The food product packaging materials typically may include plastic films, foil wrapping, or paper-based packaging materials. In practice, food products are introduced into the packaging material and the packaging material is then sealed to include the food product. Conventionally, many methods may be employed to seal the packaging material.
Traditionally, food product packaging materials may be sealed using either cold glue-based sealing methods or thermal-based sealing methods. Cold glue sealing typically involves the activation, for example by pressure, of a cold-glue adhesive that has been pre-applied to the edges of the packaging material. In practice, the packaging material may be formed into a desired shape to include the food product. In order to seal the packaging material, the packaging material is typically passed through a sealing apparatus. The sealing apparatus typically applies pressure to the edges of the packaging material to which the cold glue has been pre-applied. The pressure applied by the sealing apparatus activates the cold glue on the edges of the packaging material, causing the edges of the packaging material containing the cold glue to adhere and seal the food product packaging. Cold glue based sealing typically produces seals of sufficient strength for food product packaging applications. A seal of sufficient strength for food product applications is typically strong enough to hold the edges of the packaging material together during transport and handling, but able to be cleanly pulled apart by humans opening the package.
Unfortunately, the traditional cold glue based sealing method includes some significant drawbacks, including discontinuity and interruptions in packaging. For example, a significant problem encountered in cold glue based sealing is the formation of defective seals. For example, a defective seal may occur when an inadequate amount of cold glue is pre-applied to the packaging material. When an inadequate amount of cold glue is pre-applied to the packaging material the edges of the packaging material may not completely adhere together. If the edges of the packaging material do not completely adhere together, air may enter the package and have adverse effects on the food product. Another problem that may occur with cold glue based sealing is when the pressure applied to the edges of the packaging material including the cold glue is not sufficient to activate the cold glue. When the cold glue is not sufficiently or completely activated, the edges of the packaging material may peel away from each other, thus compromising the integrity of the seal. Proper seal integrity is when there are no channels in the seal between the outside of the packaging and the inside of the packaging. When the integrity of the seal is compromised, air enters the packaging and may negatively impact the food product quality. Typically, costly protective barriers are inserted into the laminated field. The barriers, or seals, are used to protect the integrity of the product enclosed within the sealed package. However, the barriers may be wasted if channeling occurs.
A further drawback typical in cold glue based sealing is that extremely precise alignment of the edges of the packaging material is typically required to form a proper seal. If the edges of the packaging material are not precisely aligned when they pass through the sealing apparatus, air pockets or wrinkles in the packaging may form “channels” in the seal. Channels are gaps in the seal through which air can enter the packaging material. As mentioned above, the introduction of air into the packaging may negatively impact the quality of the food product.
An additional drawback to cold glue based sealing is that the cold glue may be sensitive to atmospheric changes in the processing plant. For example, if the temperature or humidity in the plant reaches a critical level, the cold glue may become partially activated, causing the cold glue to adhere to an undesired surface, such as a roll or sheet feeding the packaging material. When the cold glue is prematurely activated and adheres to an undesired surface, the overall speed of the packaging process may be adversely affected, for example, by shutdown of the packaging process.
A further drawback of cold glue sealing is that cold glue sealing requires that the packaging material be sealed with a fairly wide seal. For example, a cold glue seal may require a seal of 10-15 millimeters in order to maintain the necessary integrity of the seal. Because a cold glue seal requires a relatively large seal, the seal requires a significant proportion of the total packaging material required to package the food product. Additionally, components of the system may become jammed during the packaging process. Thus, downtime in the system may occur due interruptions in the system.
The second traditional method of sealing food product packaging materials is thermal-based sealing. Typically, in thermal sealing, no adhesive is applied to the packaging material. Instead, the packaging material is sealed by passing the packaging material between a heated pair of jaws. The pair of jaws are typically heated using thermal conduction, for example, an electric current may be passed through a heating element mounted on the pair of jaws to heat the jaws. As the edges of the packaging material pass between the heated pair of jaws, the edges partially melt and adhere to each other.
Thermal sealing also suffers from a number of drawbacks. For example, thermal sealing is typically a relatively slow process compared to glue-based sealing. Thermal sealing is slow because the edges of the packaging material must be heated enough to melt to form a seal, requiring a relatively longer time. Thermal sealing may, however, provide some advantages to glue-based sealing. For example, a thermal seal may provide for greater seal integrity than provided using glue-based sealing. However, thermal sealing is typically at least an order of magnitude slower than glue-based sealing. Further, the glue seals typically are sensitive to the presence of food material in the seal area. The presence of food material within the seal area typically disrupts the seal. Thus, conventional packaging material sealing applications are often forced to choose between integrity of the seal and speed of formation of the seal.
Ultrasonic sealing may be employed to overcome some of the drawbacks inherent in cold glue-based sealing or thermal-based sealing. Typically, in ultrasonic sealing, ultrasonic energy, instead of conductive heat or an adhesive, is applied to the packaging materials to be sealed. The injection of ultrasonic energy into the packaging material typically heats the packaging material, causing the packaging material to partially melt and adhere to form a seal.
Historically, ultrasonic welding was developed as an alternative to welding technologies such as glue-based or thermal-based. Generally, ultrasonic welding has been employed in various applications for some time. The use of ultrasonic welding is a well established tool for sealing applications such as thermoplastics, textiles, and more recently, food product packaging sealing.
Typically, in processes for ultrasonic sealing of packaging materials, ultrasonic energy is applied to the packaging materials by passing the packaging materials between an ultrasonically activated horn and a stationary or rotary anvil. A typical ultrasonic horn is made of a metallic material having good acoustic qualities, such as aluminum or titanium. A typical anvil is also made of metallic material such as steel or aluminum and is positioned in opposition to the ultrasonic horn. Ultrasonic vibration in the horn is typically produced by supplying oscillatory electrical energy from an external power supply to an electromechanical transducer or converter, such as a piezoelectric crystal, which transforms the electrical energy into mechanical vibration. Typically, the mechanical vibration is then amplified by an amplitude transformer, or booster, to a predetermined operational amplitude. The booster is typically directly connected to the ultrasonic horn and supplies the ultrasonic vibration employed by the ultrasonic horn. Typically, the ultrasonic horn vibrates at between 20 Khz and 40 Khz.
Typically, an ultrasonic seal is created when packaging material is compressed between the ultrasonically activated horn and the stationary anvil or drum. The ultrasonically activated horn exerts ultrasonic vibrational energy on the packaging material. The ultrasonic energy causes the packaging material to heat. As the packaging heats, the packaging locally melts and adheres together along a pattern typically dictated by the design of the anvil. As the locally melted packaging cools upon leaving the horn and anvil, the packaging forms an ultrasonic seal.
As mentioned above, ultrasonic sealing has many advantages over traditional cold glue-based or thermal-based sealing. In comparison to cold glue sealing for example, ultrasonic sealing typically provides more reliable seal integrity. More reliable seal integrity may be achieved using ultrasonic sealing because there is no adhesive being used in the sealing. Therefore, the problems with adhesives such as an inadequate amount of pressure not sufficiently activating the cold glue are not found in ultrasonic sealing. Furthermore, adhesive-specific problems such as channeling are not typically encountered in ultrasonic sealing. Typically, because ultrasonic sealing heats and melts the packaging material together directly, the seal integrity is greater than that of cold glue. Another advantage in ultrasonic sealing of packaging material as opposed to cold glue is that an ultrasonic seal is typically much narrower than the seal width for cold glue. This reduction in the seal width may reduce the amount of packaging material required to package a food product by reducing the proportion of the packaging material used in to form the seal. The reduction in the amount of packaging material may lead to a reduction in overall conversion costs due to reducing the total consumption of packaging material.
Ultrasonic sealing may also have a number of advantages over traditional thermal-based sealing. A first advantage ultrasonic sealing may have over thermal sealing is speed. The injection of ultrasonic energy directly into the packaging material causes the packaging material to melt and seal more quickly than thermal-based sealing.
As described above, ultrasonic sealing has been successfully employed to ultrasonically seal packaging materials. Ultrasonically sealed packaging materials typically include three seals, a front end seal, a back end seal, and a longitudinal edge seal extending from the front end seal to the back end seal. Typically, ultrasonic sealing may be employed to seal either the front and back ends, or to seal the longitudinal edge, although at least one system employs ultrasonic seal to seal both the ends and edges.
U.S. Pat. No. 4,373,982, entitled “Ultrasonic Sealing Apparatus” (the '982 patent) illustrates one apparatus for ultrasonic sealing of the longitudinal edges of a plastic film. As shown in FIG. 5 of the '982 patent, the apparatus includes a forming structure 40, an anvil 44, and an ultrasonic horn 50. In operation, a plastic film 34 is supplied to the forming structure 40. The forming structure 40 forms the plastic film 34 into a tubular shape with contiguous edges. The contiguous edges of the plastic film 34 are then passed between an ultrasonic horn 50 and a stationary anvil 44. As the edges of the plastic film 34 pass between the ultrasonic horn 50 and the stationary anvil 44, the edges are ultrasonically sealed to form a longitudinal ultrasonic seal. After the longitudinal ultrasonic seal is formed, the plastic film 34 remains stationary while traditional glue or adhesive-based sealing techniques form a front end seal and a back end seal. The apparatus of the '982 patent provides for the intermittent, non-continuous sealing of the longitudinal edges of the plastic film 34. Because of the intermittent motion of the plastic film 34, the energy imparted to the plastic film 34 by the ultrasonic horn 50 must be controlled.
U.S. Pat. No. 4,517,790, entitled “Apparatus and Method For Ultrasonic Sealing of Packages” (the '790 patent) illustrates a method for ultrasonic sealing the front ends and back ends of packaging materials. As shown in FIG. 1, the invention of the '790 patent includes an ultrasonic end-sealing assembly 46 including a packaging film F, a back up anvil 48 rotated by a rotary drive shaft 50, and an ultrasonic horn 52. In operation, the packaging film F is supplied to the ultrasonic end-sealing assembly 46. The packaging film F is then passed between a single edge ultrasonic horn 52 and a single edge back up anvil 48 to form an ultrasonic end seal. The packaging film F has already been longitudinally edge sealed. The single edge ultrasonic horn 52 moves vertically in an up-and-down motion in conjunction with the rotating single edge back up anvil 48. That is, the ultrasonic horn 52 and back up anvil 48 are synchronized to draw towards each other at a specified time, thus trapping the packaging film F and ultrasonically sealing the packaging film F to form an ultrasonic end seal. The apparatus in the '790 patent only includes an ultrasonic end-sealing unit with a single edge, vertically-moving ultrasonic horn and a single edge, rotating back up anvil.
U.S. Pat. No. 4,534,818, entitled “Method and Apparatus for Ultrasonic Sealing” (the '818 patent) illustrates a method for ultrasonically end sealing and ultrasonically longitudinally edge sealing packaging materials as part of a form and fill packaging machine. With regard to longitudinal edge sealing, the method of the '818 patent operates substantially as described above with reference to the '982 patent. With regard to end sealing, as shown in FIG. 1, the method of the '818 patent includes an ultrasonic horn 12 mounted on an upper moveable jaw 16 and an ultrasonic anvil 14 mounted on a lower moveable jaw 18.
In operation, packaging material is formed into a tubular configuration and an ultrasonically longitudinally edge sealed to form edge sealed packaging material as in the '982 patent. Next, the ultrasonically edge sealed packaging material is passed between the upper and lower moveable jaws 16, 18. The upper and lower moveable jaws 16, 18 then compress the packaging material. As the upper and lower moveable jaws 16, 18 compress, the ultrasonic horn 12 mounted on the upper moveable jaw 16 compresses the packaging material between the ultrasonic horn 12 and ultrasonic anvil 14. The ultrasonic horn 12 injects ultrasonic energy into the packaging material to form an ultrasonic end seal, as described above. The food packaging thus has now been longitudinally edge sealed and front end sealed. After the ultrasonic front end seal is created, a food product is introduced into the edge sealed and front end sealed food package. Finally, the edge sealed and front end sealed food package containing the food product is passed between the upper and lower moveable jaws 16, 18 to form a back end seal. To form the back end seal, the upper and lower moveable jaws 16, 18 clamp down on the packaging material in a similar fashion to the formation of the front end seal. The ultrasonic horn 12 mounted to the upper moveable jaw 16 contacts the packaging material and injects ultrasonic energy to form an ultrasonic back end seal. Once the back end seal has been completed, the food product package containing food product has been completely sealed. As in the apparatus of the '790 patent, in the '818 patent, the edge seal and one end seal must be created prior to introducing food product into the packaging.
As described above, one of the limitations of the prior art systems is the inability to introduce a food product item without first performing a longitudinal edge seal and at least one end seal before. Systems such as those described above, that require product packaging to be completely ultrasonically edge and end sealed, prior to introducing food product into the sealed packaging may be less than optimal for other applications. For example, performing ultrasonic edge sealing and end sealing while intermittently introducing food products into the packaging may limit the speed of the packaging process. Also, positioning food product inside the packaging without trapping any food product in the seal may be difficult.
Thus, a need exists for a faster and more efficient food product packaging system. Additionally, a need exists for a food product packaging system that combines the speed of cold glue based sealing with the seal strength and integrity of thermal based sealing. Also, a need exists for a continuous flow wrap system rather than a form and fill type packaging system.